How can Cassandra have no single point of failure when it has no master and data is not replicated but distributed?

Question

Perhaps I am misunderstanding, but the Apache Cassandra Wikipedia article says:

"Every node in the cluster has the same role. There is no single point of failure. Data is distributed across the cluster (so each node contains different data), but there is no master as every node can service any request."

How can each node contain different data, but there be no single point of failure? For instance, I would imagine that in this senario, if a node when down containing the record I was querying, then a different node would pickup that request, however, it would not have the data to satisfy it..since that data was on the node that went down..

Can someone clear this up for me?

Thanks!

Answer 1

Cassandra clusters do replicate data across the nodes. The specific number of replicas is configurable, but generally production clusters will use a replication factor of 3. This means that a given row will be stored on three different machines in the cluster. See the reference documentation on replication for more details.

In terms of servicing requests, if a node receives a request for data that it does not have it will forward that request to the nodes that do own the data.